Frangible booster motor



June 28, 1966 p E. THoMAs ETAL 3357,804

FRANGIBLE BOOSTER MOTOR Filed Feb. 4, 1964 Paul E. Thomas Giles RWefherill.

INVENToRs. W WI. By J.

JW M W c. M

` 3,257,804 Patented ,June 28,l 1966 3,257,804 FRANGIBLE BOOSTER MOTORPaul E. Thomas and Giles P. Wetherill, Huntsville, Ala., assignors tothe United States of America as represented by the Secretary of the ArmyFiled Feb. 4, 1964, Ser. No. 342,571 Claims. (Cl. 60-35.6)

The invention described herein may be manufactured and used by or forthe Government for governmental purposes without the payment of anyroyalty thereon.

The present invention relates to a means for disposing of a boostermotor after its ejection from a rocket so as to minimize the danger topersonnel' or property upon its descent to earth. In the operation ofrockets or the like it is known thatiin order to obtain suficient thrustit is oftentimes necessary to use a booster which may be dropped afteruse. When using a conventional 'booster it has been necessary to firethe rocket in isolated geographic areas so as to prevent damage orinjury caused byv the dropped booster as it returns to earth.Experiments haveindicated that a falling object with only 57 foot poundsof energy would be lethal. A freely falling booster case which may Weighhundreds of pounds thus constitutes a hazard of formidable proportions.Much experimentation has been performed in an elfortto eliminate thishazard,`thus allowing rockets to be fired over urban or even heavilypopulated geographical areas.

Our invention contemplates a booster motor case which when ejected maybe reduced to non-lethal fragments, that is, fragments having less than57 foot pounds of energy. In this design, a high strength rigid typesheet explosive such as Tacot, Octol or Monite is used as an integral-part of the motor case and, as such, the sheet materially contributesto the structural strength of the booster motor. Such sheet explosiveswill burn rather than detonate when exposed to high temperature. Theexplosive' is insulated from the internal heat of the burni-ngpropellant and from the external aerodynamic heating by layers ofinsulating material to protect the structural integrity of the materialas well-as its explosive properties.

Accordingly, on object of our invention is to provide a lbooster motorwhich will consi-stently disintegrate into minute pieces whichconstitute no hazard when falling into populated areas.

Another object of our invention is to provide a frangible booster motorhaving approximately the same dimensions and flight characteristics asa-conventional booster motor.

Still another object of' our invention is to provide a booster motorwith an explosive charge which in no way interferes with the operationor fuel capacity of a booster.

Yet another object of our invention is to provide a frangible boostermotor which is relatively simple and economical to manufacture.

This invention together with other objects and advantages thereof willbest be understood by reference to the following description andaccompanying drawing, in which:

The single figure is a cross-sectional showing the general configurationand location of each of he layers which make up the booster motor; A

Referri-ng now to the drawing the frangible booster motor 1 comprises abody 3 having a fuel chamber cylinder 5 and a nozzle portion 7. Theforward end of the cylindrically shaped fuel chamber is closed by meansof a head closure plate 9. The 'body 3 is usually fabricated from aunitary sheet of steel thus forming a rigid inner liner for the boostermotor. The characteristics of the steel used to fabricate the body, ofcourse, are quite varied i-n that it must withstand a great deal of heatwhile yet being somewhat brittle so as to disintegrate when subjected toexplosive forces.

Immedately surrounding the body 3 is an insulating layer 11 which isattached to the body and, as illustrated, conforms to the generalconfiguration of the exterior of the motor. Insulating layer 11, whichmay be made of any commercially available insulating material, such aspolyurethane or asbestos, is designed to prevent the intense heat causedby the firing of the booster from burning eX- plosive layer 13 whichsurrounds the insulating layer.

It is essential that the insulating layer be extremely effective becausealthough the gradual application of heat will not necessari-ly explodelayer 13 it will cause deterioration .or burning thus rendering theexplosive layer inoperative as an explosive as well as drasticallyreducing its structural strength and therefore the strength of the motoritself. A film of igniter material 15 entirely surrounds layer 13 toassure instantaneous and complete ignition of the explosive upon asignal from an igniter mechanism 17. A cord or strip type ignitermaterial may also be used to ignite the eXplosive layer. Ignitermaterial 15 is surrounded by an exterior heat Shield 19 which alsoconforms to the general 'configuration of the booster motor. Thisshield, which may be made of any commercially available insulatingmaterial, such as polyurethane or asbestos, is provided to protect theigniter material and the explosive layer from heat generated byaerodynamic friction as the rocket passes through the atmosphere. Sincethe heat shield is located on the exteri'or of the explosive itscharacteristics must make it extremely resistant to heat while yet itmust be quite frangible since its fragments may be blown clear withoutreceiving a great deal of force from the explosive. lThe device isdesigned so as to locate the explosi-ve completely around and on theexterior of the main booster body so as to exert a great deal of forcetoward the interior. By locating the explosive on the exterior of themotor body the fragments are blown inwardly from each side of thebooster. These fragments are thus vi'olently thrown together in themiddle area of the booster and broken into small pieces which will floatharrnlessly back to the earth.

In operation of the device, the booster motor will be attached to arocket and will -be dropped therefrom after its fuel is expended. Atiming mechanismmay be built into the igniter mechanism 17 to 'allow alapse of time between dropping of the booster and ignition of theexplosive in the booster so as to avoid interference with the flight ofthe rocket. Igniter mechanism 17 will then actuate the igniter film orstrip whichin turn will set off explosive layer 13. The explosive layerbeing confined between the exterior heat Shield 19 and the body 3 willcause a uniform force upon the entire area of each of these elementsthus causing them to disintegrate in small approximately equal particleswhich will fall harmlessly to the earth.

It will thus be seen that our invention provides a frangible boostermotor which because of the use of high strength rigid type explosive isequal to conventional boosters in all essential design characteristicsand yet is completely safe for firing over populated areas.

While the foregoing is a description of a preferred embodiment, the.,following claims are i'ntended to include those modifications andvariations that are 'within the spirit and scope of our invention.

We claim:

1. A frangible booster motor comprising: a generally cylindricallyshaped body having a fuel chamber i-n one end thereof and an open nozzleat the other, a layer of heat resistant insulating material adjacent toand conforming to the configuration of said body, a layer of rigid highstrength sheet explosive completely surrounding and conforming to theshape of said body and being located immediately on the exterior of saidinsulating layer, igniter material immediately adjacent said explosive,an exterior heat shield surrounding the device and conforming to theconfiguration thereof, and means for igniting said igni'ter material.

2. A device as set forth in claim 1 wherein said igniter materialcomprises a film completely surrounding and immediately adjacent saidexplosive layer.

3. A'device as set forth in claim 2 Wherein said igniter means comprisesa primer cord.

4. A frangible booster motor comprsing: a generally cylindrically shapedbody having a fuel Chamber and a nozzle portion, an explosive sheetcompletely surrounding said body and insulated from said body, and meansdisposed exterio-rly of said explosive sheet for igniting said explosiveSheet, said means including a film of igniter material completelysurrounding and immediately ad- UNITED STATES PATENTS 2,937,595 5/1960Margulis et al.

3,013,333 12/1961 Burke 102- 23 X 3,017,746 1/1962 Kiphart 60-3563,017,836 1/1962 Guay 60 35.6 3,062,l42 11/1962 Breza et al. 102-23 MARKNEWMAN, Primary Examner.

C. R. CROYLE, Assistant Examiner.

1. A FRANGIBLE BOOSTER MOTOR COMPRISING: A GENERALLY CYLINDRICALLYSHAPED BODY HAVING A FUEL CHAMBER IN ONE END THEREOF AND AN OPEN NOZZLEAT THE OTHER, A LAYER OF HEAT RESISTANT INSULATING MATERIAL ADJACENT TOAND CONFORMING TO THE CONFIGURATION OF SAID BODY, A LAYER OF RIGID HIGHSTRENGTH SHEET EXPLOSIVE COMPLETELY SURROUNDING AND CONFORMING TO THESHAPE OF SAID BODY AND BEING LOCATED IMMEDIATELY ON THE EXTERIOR OF SAIDINSULATING LAYER, IGNITER MATERIAL IMMEDIATELY ADJACENT SAID EXPLOSIVE,AN EXTERIOR HEAT SHIELD SURROUNDING THE DEVICE AND CONFORMING TO THECONFIGURATION THEREOF, AND MEANS FOR IGNITING SAID IGNITER MATERIAL.